I have a Voodoo 3 3000 that overheats after a little while and puts multicolored artifacts all over the screen. It can work for a while, though. I've never tried to attach a fan to a V3 because I didn't want to rip the heatsink off the silicon. It turns out that those brass pins securing the heatsink to the PCB come out pretty easily.

I decided to attach an old CPU fan with zip ties that would fit through the 2.5mm holes where the pins were. I had to use five zip ties (they were short, so I had to make two long ones out of the five). I used a hole closer to the slot cover as another anchor point. It's kind of ugly, but the fan fits snugly on the heatsink without any ratting. I was able to run a 3dmark99 benchmark and do a few other tasks before the card started artifacting again. But I may do this for my fully-functioning V3s in the future.

A neater solution is to pass the "tail" of a zip tie through the fan and heatsink. The fan is held by the "head" of the zip tie.
Then secure it with the "head" of another zip tie on the backside of the card.
Snip off the excess "tails".

You can apply nuts (M3 or M4) into the cooler, so that the Fan is fixed via bolts - two should be enough

1. chose a fan, which fits onto the heatsink - would suggest 45mm / 50mm or 60mm - and mark the holes in the deeps of the heatsink
- the holes should nearly fit into the middle of the deeps
2. chose nuts which scarce dont fit into the deeps of the heatsink
3. if the nuts are too wide, grind two oposite sides of the nuts, so that is scarce dont fit into the deeps
4. do the nuts into the freezer and heat the heatsink with a hairdryer
5. apply the cold nuts into the the ground (important) of the hot deeps (should fit now) - do it fast!
6. Take Bolts (fitting the nuts) and shorten them, so that they dont touch the ground of the heatsink with applied fan
7. the bolts must not touch the ground - take washers if the bolts ar too long